1. Field
Disclosed herein is a tire for a handling vehicle, designed to transport heavy loads, over short distances and at low speeds, such as, for example, a materials-handling vehicle used in an underground mine. It relates more precisely to a mounted assembly consisting of a tire mounted on a rim.
A further subject of the invention is a method for producing such a mounted assembly.
2. Description of Related Art
Handling vehicles are often equipped with solid tire instead of conventional inflated tires. A solid tire is an object of toroidal shape, most frequently made of rubber, designed to be mounted on a wheel, but with no internal cavity designed to be inflated with an inflation gas. The load applied to the solid tire is supported by the structure of the solid tire.
A solid tire has a certain number of advantages over an inflated tire. First, because there is no inflation gas, it can neither deflate nor burst, which ensures an advantage in terms of reliability and safety. Then, a solid tire, because of its damping capacity that is greater than that of an inflated tire, contributes to better dynamic stability of the handling vehicle during loading and unloading operations which cause dynamic load transfers between the front and rear axles of the vehicle. Moreover, a solid tire has a considerable load capacity because of its high vertical rigidity and a reduced space requirement relative to an inflated tire having the same load capacity. Finally, a solid tire requires reduced maintenance: because there is no inflation gas, there is no pressure to check.
On the other hand, a solid tire has certain drawbacks relative to an inflated tire with the same load capacity. First, a solid tire has a higher weight because of its solid structure. Moreover, its solid structure dissipates more heat, in use under the action of the mechanical stresses, which implies constraints of usage under load, speed and duration of use. Its service life with respect to wear is less than that of an inflated tire because the distribution of the pressures on the ground, in the contact surface with the ground of the tread of the solid tire, is less optimized. It costs more to manufacture because of a greater volume of material. Its environmental impact is considerable, because a worn solid tire, at the end of life, constitutes a heavy and voluminous waste product that is more difficult to recycle. Finally, the mounting of a solid tire on a rim may require specific mounting equipment that is essential for ensuring sufficient tightness on the rim to provide an effective transmission of torque.
A conventional tire comprises a tread designed to come into contact with a ground, two sidewalls extending radially inwards from the ends of the tread, and two heads extending the sidewalls radially inwards and in contact with a rim. When it is mounted on a rim to form a mounted assembly, the tread, the two sidewalls, the two beads and the rim delimit an internal cavity.
A conventional tire, of which the internal cavity is at least partly filled by a solid filling component, is a worthwhile alternative to the solid tire. Various technical solutions of this type have been proposed.
A first family of technical solutions is based on a filling of the internal cavity of the tire with concentric layers of polymeric materials. Documents WO 9703850 and U.S. Pat. No. 6,578,613 describe a tire of which the internal cavity is filled with a solid filling component consisting of concentric layers of polymeric material optionally comprising expansion joints. Document U.S. Pat. No. 7,678,216 proposes a tire of which the internal cavity contains a core made of solid material enveloped in an elastomeric foam.
A second family of technical solutions is based on a filling of the internal cavity of the tire with a material of the polymeric foam type comprising cavities or cells. U.S. Pat. Nos. 3,022,810, 3,381,735, 3,866,652, 3,907,018 and 4,060,578 describe tires of which the internal cavity is filled with a cellular elastomeric foam material of which the cells optionally contain a pressurized gas.
A third family of technical solutions is based on a filling of the internal cavity of the tire with particles of rubber mixed with a linking agent, before insertion into the tire, the mixture being designed to harden, in particular by curing, in order to form a one-piece solid filling component. Document U.S. Pat. No. 1,097,824 discloses a tire of which the internal cavity is filled with elastic solid particles such as particles of vulcanized rubber, connected together permanently by a linking material, such as a vulcanized rubber cement. Document JP 57058501 describes a solid tire made from a tire filled with a vulcanized mixture of rubber powder and liquid polyurethane, Documents JP 2001252989 and JP 04088168 describe methods for manufacturing a solid tire based on a conventional tire by filling the latter with recycled rubber powder which is mixed, before insertion into the tire, with a linking agent such as for example a polyurethane or phenol resin, the mixture thus formed being hardened, inside the tire, to form a one-piece filling component.
The foregoing technical solutions all describe a solid filling component of the internal cavity of the tire, consisting either of a one-piece element, such as a cellular polymeric foam or a vulcanized mixture of rubber particles, or of a limited number of elements, such as concentric layers of polymeric material. The design and manufacture of such solid filling components however have a certain degree of complexity.
Furthermore, the solid filling component has a mechanical rigidity which, with the structural rigidity of the tire on its own, contributes to the vertical rigidity of the tire filled with the filling component. The choice of the rigidity of the solid filling component makes it possible to adjust the vertical rigidity of the tire filled with the solid filling component, hence the relative flexing of the tire, for a given vertical load applied to the tire, to the desired level. The relative flexing of the tire is defined by the ratio of the variation of the radial height of the tire over half the difference between the external diameter of the tire and the maximum diameter of the rim measured on the edge of the rim, the external diameter of the tire being measured while static in an unloaded state.
After adjusting the rigidity of the solid filling component in order to obtain the desired vertical rigidity of the tire, it is difficult to change it, for example if there is a significant variation in the vertical load applied to the tire, without totally changing the solid filling component.